path: root/doc/switch.n

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'\" Copyright (c) 1993 The Regents of the University of California.
'\" Copyright (c) 1994-1997 Sun Microsystems, Inc.
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'\" RCS: @(#) $Id: switch.n,v 1.5 2000/09/07 14:27:51 poenitz Exp $
'\" 
.so man.macros
.TH switch n 7.0 Tcl "Tcl Built-In Commands"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
switch \- Evaluate one of several scripts, depending on a given value
.SH SYNOPSIS
\fBswitch \fR?\fIoptions\fR?\fI string pattern body \fR?\fIpattern body \fR...?
.sp
\fBswitch \fR?\fIoptions\fR?\fI string \fR{\fIpattern body \fR?\fIpattern body \fR...?}
.BE

.SH DESCRIPTION
.PP
The \fBswitch\fR command matches its \fIstring\fR argument against each of
the \fIpattern\fR arguments in order.
As soon as it finds a \fIpattern\fR that matches \fIstring\fR it
evaluates the following \fIbody\fR argument by passing it recursively
to the Tcl interpreter and returns the result of that evaluation.
If the last \fIpattern\fR argument is \fBdefault\fR then it matches
anything.
If no \fIpattern\fR argument
matches \fIstring\fR and no default is given, then the \fBswitch\fR
command returns an empty string.
.PP
If the initial arguments to \fBswitch\fR start with \fB\-\fR then
they are treated as options.  The following options are
currently supported:
.TP 10
\fB\-exact\fR
Use exact matching when comparing \fIstring\fR to a pattern.  This
is the default.
.TP 10
\fB\-glob\fR
When matching \fIstring\fR to the patterns, use glob-style matching
(i.e. the same as implemented by the \fBstring match\fR command).
.TP 10
\fB\-regexp\fR
When matching \fIstring\fR to the patterns, use regular
expression matching
(as described in the \fBre_syntax\fR reference page).
.TP 10
\fB\-\|\-\fR
Marks the end of options.  The argument following this one will
be treated as \fIstring\fR even if it starts with a \fB\-\fR.
.PP
Two syntaxes are provided for the \fIpattern\fR and \fIbody\fR arguments.
The first uses a separate argument for each of the patterns and commands;
this form is convenient if substitutions are desired on some of the
patterns or commands.
The second form places all of the patterns and commands together into
a single argument; the argument must have proper list structure, with
the elements of the list being the patterns and commands.
The second form makes it easy to construct multi-line switch commands,
since the braces around the whole list make it unnecessary to include a
backslash at the end of each line.
Since the \fIpattern\fR arguments are in braces in the second form,
no command or variable substitutions are performed on them;  this makes
the behavior of the second form different than the first form in some
cases.
.PP
If a \fIbody\fR is specified as ``\fB\-\fR'' it means that the \fIbody\fR
for the next pattern should also be used as the body for this
pattern (if the next pattern also has a body of ``\fB\-\fR''
then the body after that is used, and so on).
This feature makes it possible to share a single \fIbody\fR among
several patterns.
.PP
Beware of how you place comments in \fBswitch\fR commands.  Comments
should only be placed \fBinside\fR the execution body of one of the
patterns, and not intermingled with the patterns.
.PP
Below are some examples of \fBswitch\fR commands:
.CS
\fBswitch\0abc\0a\0\-\0b\0{format 1}\0abc\0{format 2}\0default\0{format 3}\fR
.CE
will return \fB2\fR, 
.CS
\fBswitch\0\-regexp\0aaab {
	^a.*b$\0\-
	b\0{format 1}
	a*\0{format 2}
	default\0{format 3}
}\fR
.CE
will return \fB1\fR, and
.CS
\fBswitch\0xyz {
	a
		\-
	b
		{
		# Correct Comment Placement
		format 1
	}
	a*
		{format 2}
	default
		{format 3}
}\fR
.CE
will return \fB3\fR.

.SH "SEE ALSO"
for(n), if(n), regexp(n)

.SH KEYWORDS
switch, match, regular expression